A recent study determined that there are dozens of little-researched species of rodents that are likely to be carriers of infectious human diseases—and that a surprising amount of them are concentrated in Kansas and Nebraska.

The paper, titled “Rodent reservoirs of future zoonotic diseases” and published in the Proceedings of the National Academy of Sciences, looks at the shared traits of rodents that are known carriers of disease that affect humans, and uses that profile to figure out which other species could pose a threat. Those rodent species, the report authors say, are the ones we should be paying attention to.

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Lead author Barbara Han, of the Cary Institute of Ecosystem Studies, told Fusion in a phone interview that rodents who reach sexual maturity early and tend to reproduce young, fast and often, are the most likely carriers of human disease. “Basically,” she said, the researchers were “looking at the rest of the species and saying ok, which of you guys look just like the guys that we already know about.”

Overall, there are 2,277 rodent species throughout the world, and 217 known to carry zoonoses, or infectious diseases that affect animals but can be transmitted to people. Of these, the researchers found that 150 species are likely to carry more than one zoonosis—these are the species the authors suggest we take a close look at, to determine the threats they might pose.

The researchers mapped out where all predicted and known carrier species are and found a hotspot in the American Midwest.

Map from “Rodent reservoirs of future zoonotic diseases.”The Proceedings of the National Academy of Sciences

According to the map, the two relevant species that occupy this territory are the Microtus Montanus, commonly known as the Montane vole, and the Onychomys leucogaster, known ominously as the Killer mouse (and not-so-ominously as the Northern grasshopper mouse.) They, like gerbils, are actually pretty cute…

… although the killer mouse is a wolf-like carnivore immune to scorpion bites:

Han said that the Nebraska-Kansas hotspot was somewhat surprising. “These couple of species that are overlapping in the Midwest, they’re not unknown to us, but just because something lives in your backyard, doesn’t mean that you know everything about it.”

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So, are these the most likely harbingers of the next plague? Not specifically, said Han. “We provided a first step towards a watch list… [but] just because we have a watch list it doesn’t mean all of the species are going to be high-risk to us.” Some, she said, could have low levels of human contact, or be rare.

Still, it wouldn’t be unimaginable for a pandemic to be brought on by rodents: “There is an awareness among the public health world that animals that migrate, animals that have a very wide geographic distribution, groups of species that are particularly well-adapted, cosmopolitan species that have no trouble adapting to our lifestyle… could pose the greatest risk.” But, she said, “it’s hard to say from the results of this study which species that would be.”

In any case, said Han, the number of rodent species known to carry infectious disease is “conservative.” Comforting, right?